Alkyl 3-alkoxypropionates



United States Patent ALKYL 3-ALKOXYPROPIONATES William Joseph Fox, Cottingham, England, assignor to The Distillers Company Limited, Edinburgh, Scotland, at company of Great Britain No Drawing. Application May 9, 1958 Serial No. 734,103

Claims priority, application Great Britain May 16, 1957 6 Claims. (Cl. 260-484) The present invention relates to the production of alkoxy-substituted esters, which have solvent or plasticising properties or which may be used as valuable intermediates in the preparation of other organic compounds, and in particular to the production of alkyl B-alkoxypropionates.

It is known that alkyl 3-alkoxypropionates may be produced from the corresponding dialkoxymethanes by reaction with ketene in the presence of acid catalysts such as sulphuric acid, zinc chloride and aluminium chloride; boron trifluoride and its addition products with others have also been used. The catalysts have been employed in concentrations from about 0.2% to 100% by weight based on the weight of the dialkoxymethane. By using these known processes, however, considerable quantities of undesirable by-products, such as alkyl acetates and alkoxymethyl acetates may be formed, which, if present in the product, render difiicult the purification of the desired alkyl 3-alkoxypropionate.

Furthermore, it has hitherto been believed that it is necessary to carry out the reaction between ketene and the dialkoxymethane at a low temperature, for example one in the range from 80 to 0 C., in order to obtain a reasonably good yield of the desired alkyl 3-alkoxypropionate. It has now surprisingly been found that the yield of the product obtained may be increased by carrying out the reaction at a more elevated temperature.

It is an object of the present invention to provide an improved process for the production of alkoxy-substituted esters of this type.

Accordingly, the present invention is a process of producing an alkyl 3-alkoxypropionate which comprises contacting a symmetrical dialkoxymethane with ketene under substantially anhydrous conditions at a temperature in the range from 10 to 60 C. and in the presence as catalyst of not more than by weight of boron trifluoride based on the weight of the dialkoxymethane.

The dialkoxymethane used in the process of the inven tion is a symmetrical formal such as dimethoxymethane or diethoxymethane.

The reaction of the dialkoxymethane with ketene may therefore be represented as follows:

where R signifies an alkyl group.

The dialkoxymethane is conveniently one which is a liquid under the conditions of the reaction. While the alkyl groups present in the dialkoxymethane may be other members of the homologous series, for instance they may be normal n-propyl, isopropyl, n-butyl, isobutyl, or higher group, the preferred dialkoxymethanes are dimethoxymethane and diethoxymethane. The alkyl 3- alkoxypropionates produced from these preferred compounds by the process of the invention are methyl 3- methoxypropionate and ethyl 3-ethoxypropionate, respectively.

The process of the invention is carried out under substantially anhydrous conditions, by which is meant in this specification that not more than about 0.1% by weight of water is present in the reaction mixture. The presence of proportions of water exceeding this figure is detrimental to the process in that the yield of the pure desired product is decreased, and in that the amount of alkyl acetate or alkoxymethyl acetate formed as byproducts is increased.

The reaction between the dialkoxymethane and ketene is carried out at a temperature in the range from 10 to 60 C. and preferably at a temperature in the range from 35 to 55 C. The temperature employed in the reaction depends to some extent on the nature of the particular dialkoxymethane used: for example if the reaction is carried out with dimethoxymethane, the temperature used is preferably not greater than about 44 C.

The process of the invention is readily effected at normal atmospheric pressure and may conveniently be carried out by bubbling the ketene through a mixture of the dialkoxymethane and the catalyst, the mixture being continuously stirred. Superatmospheric pressure may however be used if desired. The proportions of ketene and dialkoxymethane used are not critical; conveniently the molar proportions of ketene to dialkoxymethane are in the range from 0.5 :1 to 09:1. The process may be carried out either batchwise or in a continuous manner.

The boron trifluoride used as catalyst may conveniently be employed as a boron trifluoride-diethyl other complex consisting of approximately equimolecular proportions of boron trifluoride and diethyl ether. A suitable complex may be prepared, for example, by passing anhydrous boron trifluoride into diethyl ether maintained at a low temperature; a complex may however be obtained commercially. The proportion of boron trifluoride used as. catalyst in the reaction is not more than 5% by weight and preferably not more than 2.5% by weight based on the weight of the dialkoxymethane.

The alkyl 3-alkoxypropionate product is preferably recovered from the reaction mixture by fractional distillation after rendering the mixture alkaline by the addition of a suitable basic material such as ammonium hydroxide and separation of the aqueous phase.

In the following examples which are given to illustrate the process of the invention, parts by weight shown therein bear the same relationship to parts by volume as do kilograms to litres. The percentages shown are expressed by weight.

Example 1 65.0 parts by weight of ketene were bubbled through 196.1 parts by weight of diethoxymethane, containing 6.1 parts by weight of a boron trifiuoride-diethyl ether com plex consisting of approximately equimolecular proportions of boron trifiuoride and diethyl ether, maintained at a temperature of 35 to 40 C., the mixture being continuously stirred. .The reaction mixture thus contained 1.5% byweight of boron trifluoride based on the weight of the diethoxymethane.

When addition of the ketene was completed, the mixture was rendered alkaline by adding 15 parts by volume of ammonia solution (specific gravity 0.88) and 15 parts by volume of water. The ethyl S-eithoxypropionate product, which was obtained in a yield of based on the ketene, was removed from the reaction mixture and purified by fractional distillation. Only a trace of ethyl acetate was found to be present in the reaction mixture.

Example 2 The process of Example 1 was repeated at a reaction temperature of 15 to 20 C. and using a concentration of boron trifluoride of 0.8% by weight based on the weight of diethoxymethane, the addition of the ketene based on the ketene.

3 and the recovery and purification of the product being carried out in the same way.

A yield of 83% ethyl B-ethoxypropionate was obtained Example 3" The process of Example 1, Was repeated at a reaction temperature of 45 to 50 C. and using a concentration of boron trifiuoride of 0.5% by weight based on the weight of diethoxymethane, the addition of the ketene and the recovery and purification of the product being carried out in the same Way.

A yield of 96% ethyl 3-etl1oxypropionate was obtained based on the ketene.

Example 4 60.2 parts by weight of ketene were bubbled through 199.3 parts by weight of diethoxymethane, containing 20.0 parts by weight of a boron trifiuoride-diethyl ether complex, consisting of approximately equimolecular proportions of boron trifluoride and diethyl. ether, maintained at a temperature of 10 to 16 C.. the mixture being continuously stirred. The reaction mixture thus contained 4.8% by weight of boron trifluoride based on the weight of the diethoxymethane.

When addition of the ketene was completed, the mixture was made alkaline by adding 30.0 parts by weight of anhydrous sodium carbonate. .The' ethyl 3-ethoxypropionate produced, which was obtained in a yield of 95% based on the ketene, was removed from the reaction mixture andpurified by fractional distillation. Only a trace of ethyl acetate was found to be present in the reaction mixture.

As a comparison with the process of the present invention, the procedure described in the above Examples 1 to 4 was repeated at reaction temperatures below 10 C. The results are'given in the following table.

Reaction Percent Percent by weight of boron tritluoride 1 temperature yield of (*C.) product on ketene 0.5... -5 too 41 1.0... -5 to 43 Based on the weight of the diethoxymethane.

The improvement in yield brought about bythe use of the process of the present invention, instead of employing the lower reaction temperatures previously used,v is thus clearly demonstrated.

Example 40.0 parts by weight of ketene were bubbled through a mixture of 160.1 parts by weight of dimethoxymethane and 3.3 parts by weight of a boron trifluoride-diethyl ether complex consisting of approximately equimolecular proportions of boron trifiuoride and diethyl ether, maintained at 35 C., the mixture being continuously stirred. The

, reaction mixture thus contained 1.0% by weight of boron Example 6 50.7 parts by weight of ketene were absorbed in a mixture of 199.8 parts by weight of di-n-butoxymethane and 4.3 parts by weight of a boron trifluoride-diethyl other complex consisting of approximately equimolecular proportions of boron trifluoride and diethyl ether, maintained at 50 to 55 C.,,the,mixture being continuously stirred.

When the addition of the ketene was completed, the mixture was rendered alkaline by the addition of 12.5 parts by volume of ammonia solution (specific gravity 0.88) and 12.5 parts by volume of water. Two phases formed and were separated, the upper, organic phase yielding 218.0 parts by weight of n-butyl 3-n-butoxypropionate on distillation.

The yield of. n-butyl 3-n-butoxypropionate obtained was 89.4% based on the ketene.

As a comparison with the process of'the present invention, the procedure described in the above Example 6 was repeated at a reaction temperature below 10 C.

31.1 parts by weight of ketene were absorbed in a mixture of 200.6 parts by weight of di-n-butoxymethane and 4.2 parts by weight of a boron trifluoride-diethyl ether complex consisting of approximately equimolecular proportions of boron trifluoride and diethyl ether, maintained at -5 to 0 C., the mixture being continuously stirred.

When the addition of the ketene was completed, the mixture was rendered alkaline by the addition of 12.5 parts by volume of ammonia solution (specific gravity 0.88) and 12.5 parts by volume of water. Two phases formed and were separated, the upper, organic phase yielding 62.3 parts by weight of n-butyl 3-n-butoxypropionate on distillation. The yield of n-butyl 3-n-butoxypropionate obtained was thus only 41.6% based on the ketene.

The improvement in yield brought about by the use of the process of the present invention, instead of employing the lower reaction temperatures previously used, is thus clearly demonstrated.

I claim:

1. A process of producing a lower alkyl 3-(lower) alkoxypropionate which comprises contacting a symmetrical di-(lower)alk0xymethane with ketene under substan tially anhydrous conditions at a temperature in the range from 10 to 60 C., and in the presence as catalyst of not more than 5% by weight of boron trifiuoride based on the weight of the di(lower)alkoxymethane.

2. The process claimed in claim 1 wherein the di- (lower) alkoxymethane is dimethoxymethane and the lower alkyl 3-'(lower)alkoxypropionate. is methylS-methoxypropionate.

3. The process claimed in claim 1 wherein the di- (lower) alkoxymethane is. diethoxymethane and the lower alkyl 3-(lower)alkoxypropionate is. ethyl 3-ethoxypropionate.

4. The process claimed in claim 1 wherein the di- (lower)alkoxymethane is contacted with ketene at a temperature in the range from 35 to 55 C.

5. The process claimed in claim 1 wherein the molar proportions of ketene to di-i(lower)alk oxymethane are in the range from. 0.5:1 to 09:1. 7

6. The process claimed in claim 1 wherein not more than 2.5% by weight of boron trifluoride is present based on the weight of the di (lower) alkoxymethane.

OTHER REFERENCES Sorrn etal; Chem. Abs. 49, (1955). 

1. A PROCESS OF PRODUCING A LOWER ALKYL 3-(LOWER) ALKOXYPROPIONATE WHICH COMPRISES CONTACTING A SYMMETRICAL DI-(LOWER) ALKOXYMETHANE WITH KETENE UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS AT A TEMPERATURE IN THE RANGE FROM 10* TO 60* C., AND IN THE PRESENCE AS CATALYST OF NOT MORE THAN 5% BY WEIGHT OF BORON TRIFLUORIDE BASED ON THE WEIGHT OF THE DI-(LOWER) ALKOXYMETHANE. 